Testing Real or Complex Roots: y=g(x)D^{k}f(x)

In summary, there is a test to determine if a function has real or complex roots. One way is to check if the function is always positive or always negative. In the case of ##y = \exp(x^2) + 1##, the function is always positive, so it has no real roots.
  • #1
Karlisbad
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For the function ## y=f(x) ## is there a test to prove if its roots are real or either has some complex roots?, or in more general cases:

## y=g(x)D^{k}f(x) ## k>0 and a real D=d/dx number.:rolleyes: :rolleyes:

The question is that sometimes it can be very deceiving to tell if a function has real or complex roots, for example:

## y=exp(2 \pi x)-1 ## has only real roots.. but for real x the function ## y=exp(x^2)+1 ## has only complex roots , but for every real x the function is real.
 
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  • #2
Karlisbad said:
For the function ## y=f(x) ## is there a test to prove if its roots are real or either has some complex roots?, or in more general cases:

## y=g(x)D^{k}f(x) ## k>0 and a real D=d/dx number.:rolleyes: :rolleyes:

The question is that sometimes it can be very deceiving to tell if a function has real or complex roots, for example:

## y=exp(2 \pi x)-1 ## has only real roots.. but for real x the function ## y=exp(x^2)+1 ## has only complex roots , but for every real x the function is real.
A simple test is whether the function is always positive or is always negative. In your second example, ##y = \exp(x^2) + 1##, ##x^2 \ge 0## for all real x, and ##\exp(x^2) \ge 1## for all real x, so adding 1 makes ##\exp(x^2) + 1 \ge 2##. Therefore, this function can't have any real roots.
 

Related to Testing Real or Complex Roots: y=g(x)D^{k}f(x)

1. What is the purpose of testing for real or complex roots in a function?

The purpose of testing for real or complex roots in a function is to determine the values of x that make the function y=g(x) equal to 0. These values are important in understanding the behavior and properties of the function.

2. How do you test for real or complex roots in a function?

To test for real or complex roots in a function, you can use methods such as factoring, the quadratic formula, or the rational root theorem. These methods will help you find the values of x that make the function equal to 0.

3. What is the difference between real and complex roots?

Real roots are values of x that make the function y=g(x) equal to 0 and can be represented on the real number line. Complex roots, on the other hand, are values of x that make the function equal to 0 but cannot be represented on the real number line. They involve the use of imaginary numbers.

4. Why is it important to consider both real and complex roots?

It is important to consider both real and complex roots because they can provide important information about the behavior and properties of a function. For example, the number of real and complex roots can tell us about the number of x-intercepts and the symmetry of the graph of the function.

5. Can a function have both real and complex roots?

Yes, a function can have both real and complex roots. In fact, a polynomial function of degree n can have up to n complex roots, including real roots. However, a function can only have real roots if its coefficients are real numbers.

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